Telephone system



Nov. 8, 1955 J. J. `B. LAIR E'rAL TELEPHONE SYSTEM 4 Sheets-Sheet lFiled March l0, 1950 Nov. 8, 1955 J. J. B. LAIR Erm. 2,723,309

TELEPHONE SYSTEM Filed March 1o, 195o 4 sheets-sheet 2 WEQ EN hm.

0\ lll TNT INTQRNKWU lr II Q\\ S lv INVENTORS EDMOND M. OELORA//YE'JULIE/Y d. B, BY

AGENT Nov. 8, 1955 J. J. B. LAIR Erm.

` TELEPHONE SYSTEM Filad March l0, 1950 4 Sheets-Sheet 3 Illel IlTELEPHONE SYSTEM 4 Sheets-Sheet 4 Filed March 10, 1950 d. zokkabm. MMIIbn. NM. no 53.3

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United States Patent() TELEPHONE SYSTEM Julien J. B. Lair, Nutley, N.J., and Edmond M. Delorane, New York, N. Y., assignors to InternationalStandard Electric Corporation, New York, N. Y., a corporation ofDelaware Application March 10, 1950, Serial No. 148,948

8 Claims. (Cl. 179-15) cach subscriber is allocated a periodic shortinterval of q time within a transmission sequence thatcomprises all thesubscribers connected to such transmitting medium. The relative positionoccupied in the transmission sequence by a subscribers time intervalcharacterizes said subscriber. pulse is successively retarded betweenevery two subscribers sets either by the insertion of a delay line, bythe retardation resulting from losses in the cable, or by a combinationof both of these means. This arrangement makes it possible to add thesuccessive delays in series, so that, generally speaking, it is notabsolutely necessary to install delay lines in the subscriber sets forthe transmitting channel, although it may be necessary to use a smallauxiliary delay line in some subscriber sets owing to their particularlocation.

The above-described arrangement, however, has the drawback of making theposition of a subscribers time interval in the transmission sequencedepend on his geographical location. Thus the subscriber located closestto the exchange has the economical advantage of having the smallestdelay, while the subscriber located farthest away must, obviously, begiven the greatest delay.

In accordance with one of the main features of the invention, areference pulse distribution circuit is so laid out that thecharacteristic retardation of each subscriber line in the transmissionsequence does not depend on the location of the subscriber along thedistribution circuit. With this arrangement, the characteristic delay ofeach subscriber line is obtained by use of a delay line incorporated inthe subscribers substation circuit. For example, if a sequence of 102microseconds is selected for a 100- subsubscriber cable and 2microseconds are reserved for the reference pulse, each of the 100subscribersimay be allocated 1 microsecond. Subscriber No. 4 will beallocated 1 microsecond in the 5th microsecond. after the referencepulse, and subscriber No. n will be allocated a time interval in then-l-I'th microsecond after the reference pulse. The retardation linesincorporated in the subscriber sets Will then have delays of from 1 to100 microseconds, depending on the position assigned to the set involvedin the transmission sequence.

According to another feature of the invention, the subscribers of thesame group are divided into two or into a very small number n ofsubgroups rin such a way as to decrease by a factor of 2 or n the sizeof the delay lines ofthe subscriber sets having the greatest delay.v Inthis In such a system the subscribers reference ice case, although theremay be only a single cable to receive the modulated pulses, there willhave to be as many cables for transmitting the pulses to be modulated asthere are subscriber subgroups. Each of these cables will carry the samenumber of pulses per second, but the relative phase of these pulses willdepend, on the one hand, on the delay of the subscriber set forming partof the subgroup served that has the lowest delay and, on the other hand,on the differences, if any, in the cable lengths.

According to still another feature of the invention, the exchange sendsLa positive and a negative pulse every 102 microseconds (in the examplechosen) over the subscriber cables, the negative pulse being separatedfrom the positive pulse by 50 microseconds. By means of tubes ordetectors, for example, the positive pulses can be routed only to thesubscriber sets whose delay is between 0 and 50 microseconds and thenegative pulses, only to the subscriber sets having a delay of between50 and 100 microseconds. For example, if the positive pulse is used asthe reference pulse, a 50-microsecond delay will be saved in each of thesets that receive the negative pulse, the delay of which must be between50 and 100 microseconds. Upon leaving the subscriber sets, the negativepulses may, if necessary, be converted into positive pulses either byreversing the output terminals or by means of a transformer.

According to another feature of the invention, the subgrouping of thesubscribers and the transmitting of positive and negative pulses arecombined in such a way as to decrease the size of the delay lines in thesubscriber sets, thus making possible more economical operation.

According to still another feature of the invention, it is possible toreduce the size of the delay lines in the subscriber sets by sendingduring the lO2-microsecond period, a series of n pulses over the cablethat feeds all the subscriber sets. The n pulses can either be unevenlyspaced or else they may be uniformly distributed every /n microsecondsand are carried by n substantially higher frequencies, which can be sentover the cables used (e. g., television cables). The subscriber sets aredivided into n groups and either each group or each subscriber isprovided with a circuit tuned to one of the n frequencies in such a wayas to receive only the pulse that precedes the position that said groupor set occupies in the transmission sequence. Thus, the delay of thepulse of frequency fr with respect to the reference pulse of frequencyfo will make it possible to savein the lines a time interval equivalentto the delay introduced in thesubscriber sets that receive pulse f1.

The features referred to will be better understood from a reading of thefollowing detailed description with reference to the accompanyingdrawings, in which Fig. l diagrammatically illustrates a cable withwhich a plurality of subscribers stations are connected whose physicalposition does not determine theorder in which the selection of a stationmay be effected.

Fig. 2 diagrammatically illustrates the manner in which a plurality ofcables may be connected with an exchange;

Fig. 3 diagrammatically illustrates an arrangement for reducing the sizeof the delay networks provided at the substations by dividing thestations into subgroups.

Fig. 4 diagrammatically illustrates another arrangement for obtainingthe same result as in Fig. 3, by employing positive and negative pulses;

Fig. 5 illustrates an arrangement for making use of the principles ofboth Figs. 3 and 4;

Fig. 6 illustrates another arrangement for reducing the size of thedelay networks by employing carrier frequencies-for the pulses; and

Fig. 7 dagrammatically illustrates an arrangement in which an adjustabledelay network is used at the subscribers station.

Referring now to Fig. 1, a cable having lines and 11 extends from acentral exchange 12. It is assumed that one hundred telephonesubstations So to S99 are bridged across the cable lines between pointsAo, Ai, Az-Ags on line l@ and points Bo, B1, Bz-Bss on line 11. Pulsesare sent from the exchange 12 over transmitting line 10 and travel inthe direction of arrow in parallel over the different substations andback to the central exchange over receiving line 11. The line 10 isdoubled back on itself forming a return loop and the .connecting pointsAo to A99 are on the doubled back portion 10a on the line. Thus theconnecting point An of station So will be reached last by a pulsetraveling over line 10 and the connecting point Ass of station S99 Willbe 'iirst. The cable line 11, on the other hand, is straight and theconnecting point BQ thereon is the nearest and connecting point B99farthest removed from the central exchange. Therefore the path traveledby a pulse over line 10, Ass, Ses, B99, 11, will be of the same lengthas the path traveled by a pulse over line 10, 10a, A0, So, Bo, 11, orover any'of the other intervening stations, the parallel connections Ao,Bo, A1, B1-A9s, B99, being all of the same length. It `will beunderstood that in practice each line 10 or 11 will comprise a coaxialline or shielded pair.

An impulse sent out over line 10 may thus travel over one hundreddifferent stations and return as a signal pulse over line 11 to thecentral exchange 12.

However, according to the present invention there is provided at eachstation a delay network Lu, L1, Lz-Lss which delays by 0, l, 2-99 unitsof delay the passage of pulses through the corresponding station,whereby the impulse traveling over stations So will arrive rst over line'11 at station 12, the pulse traveling over station S1 second, the pulsetraveling over station S2 third, etc., and the pulse traveling overstation S99 one hundredth or last, being delayed by ninety-nine units ofdelay with respect to the pulse that traversed station So.

, Obviously the stations may be arranged in .any order without aiectingthe relative positions of the pulses traveling therethrough. Even ifstations S99 and S2 changed places, the pulse traveling over S99 wouldarrive at the exchange 99 units of delay later than the pulse over Soand 97 units later than the pulse over S2, because the delays are causedsolely by the networks Lo to L99. This permits easy changing ofsubscribers stations and their installation in any order withoutchanging the time position of the pulses traveling through theirstations.

It is to be understood that each of the stations So to Saa is providedwith means for modulating the pulse passing through it, such modulationbeing in any desired manner, to transmit intelligence from that stationto the main exchange.

In the exchange system shown in Fig. 2, the exchange 12 is shown ashaving associated therewith the cable 10, 11 arranged in the mannerdescribed in connection with Fig. l, and two other cables, one havinglines 13, 14 and the other having lines 15, 16. Each of these cables hasa plurality of stations bridged across its lines to produce the sameresult as explained in connection with Fig. 1.

In the system shown in Fig. 3, 50 delay units may be eliminated in eachtransmission line for subscribers '50 to '99. The subscribers areconnected with the exchange 12 over a cable having three lines; one line17 common to all the subscribers and a line 18 individual to subscribers0 `to 49. The third line is 19 and stations 59 to 99 are bridged acrossit and the line 17. Each of the lines 18 and 19 has its end doubled backfor the purpose explained in connection with Fig. 1.

Reference pulses 20 are applied to cable .line 18, and pulses 21, whichare .auxiliary reference pulses, are lapplied to cable line 19. Thedelay of pulse 21 with respect to 20 would -be fty microseconds -if thetwo cable lines were of the same length, but int he present case thisdelay will be shortened by the additional time required for a signal totraverse cable line 19 as compared to cable line 18. Assuming that d isthe distance between the doubled back ends of cable lines 18 and 19, theadditional distance travelled by a pulse over cable line 19 is 2d, andif the speed of propagation is V, then the additional time will be:

lf the auxiliary reference pulse 21 is retarded by a delay line byt=(50-t) microseconds, this pulse would arrive at point 22 with a delayof 50 microseconds, assuming no delay line is provided and that the unitof delay Vis l microsecond. Thus all the stations of group 50-99 willhave a delay `of lfifty `microseconds and one of these stati-ons may,for instance, be Aclassified as station 63 of the whole hundred byaccording to it a delay of 63-5-0=l3 `units instead of 63 units as wouldbe the case -for the arrangement shown in Fig. 1. The station S50 will,therefore, have 0 delay just as station S0, the station S51 will haveone unit of delay just as S1, etc., station S99 will have 49 units ofdelay just as station S49. There will be a saving of 50 50=2500 delayunits to take care of stations bridged across the same cable.

Obviously there could be other sub-divisions of the stations associatedwith the same cable as the one shown in Fig. 3, for the purpose ofreducing the maximum delay required at the stations. In practice todetermine the number of groups or subgroups a compromise will be-effected between the saving in time delay units and the cost ofvproviding additional cable lines.

The results of Fig. 3 can be obtained also by the arrangement shown inFig. 4 in which the cable line 17 is connected with all the 100stations, as Iin Fig. 3, but the other terminals of each station areconnected with the doubled back end of the same line 23. Stations 0 to49 are `connected with the line 23 over rectifiers R0, R1, etc.,-R48,R49, so -poled as to permit the passage of positive pulses from line 23to conductor 17, and stations S56 to S99 are connected over oppositelypoled rectiiiers R50, R51, etc-R98, R99. The reference pulse 20 forstations S0 to S49 will be sent as a positive vpulse whilst theauxiliary reference pulse 24 will be a negative pulse and spaced 50microseconds from the reference pulse 20. The positive reference pulses20 will pass to the stations S0 to S49 only, and the negative referencepulses only to the stations S50 to S99. All the stations of this secondgroup S50 to -S99 will thus have a permanent delay of 50 microsecondsand their position among the hundred stations can be determined byimparting only a supplementary delay thereto, e. g. 13 units to station63 instead of 63 delay units asin the case of Fig. l. Obviously thestations need not be arranged in the same order in Vwhich they are shownin Fig. 4. Station S99 with its negatively poled rectifier R99 may beadjacent to station S0 with its positively poled rectifier.

Fig. 5 shows a combination ofthe arrangements illustrated in Figs. 3 and4, the same'reference numerals being vapplied as in the two previousfigures, so as to simplify the reading of the circuit. The onlydifference is that in this arrangementthe maximum delay is 25microseconds. The cable line 18 will receive the positive referencepulse 20 followed by negative auxiliary reference pulse 24 with a delayof 25 microseconds. The subscribers S0 to S24 will receive via rectiersR0 to R24 only the positive pulses, and thesubscribers S25 to S49whichare branched across the .doubled1back end of line 18 will receiveonly the auxiliary negative pulses 24 withadelay of 25 microseconds via.rectiiers R25 to R49. Station S0 will therefore have the same delay asstation S25, station S1 the same as station S26, etc.

In the second group which are bridged across line 17 and the doubledback end of line 19, the positive reference pulses 25 will arrive with adelay of SO-t microseconds followed by a negative auxiliary pulse 26with an additional delay of 25 microseconds. v

' All the pulses will reach the second group with a 50 microsecond delayas compared to those'reaching the first group, thus effecting a savingof 50 delay units, and within the group a saving of 25 delay units willbe effected by the opposite poling of the rectifiers R50 to R74 ascompared to R75 to R99. The total saving of delay units for 100 stationswill be 50 50|2(25 X25)=3750 delay units of the 4955 units of delaywhich are necessary in-the case in the arrangement shown in Fig. l.

It will be noted that when a group is divided into a greater number of`subgroups the saving in delay units is at a decreasing rate whichexplains the compromise above referred to. f

The pulses may retain their positive or negative polarity in the outputcircuits of the stations, or they may be converted into pulses of thesame polarity, e. g. by means of transformers.

In the arrangement shown in Fig. 6, the same result is obtained as inFig. 5, by dividing the stations S0 to S99 into four equal subgroups andbridging them across cable lines 17 and 27, each over a selective wavefilter F1, F2, F3, F4. The line 27 will carry the reference pulses.These are sent at intervals of 25 microseconds, the first pulse 28 atfrequency f1, the second pulse 29 at frequency f2, the third 30 atfrequency f3, and the fourth 31 at frequency f4. The filter F1 will passonly pulses 28, filter F2 only pulses Z9, filter F3 only pulses 30, andfilter F4 only pulses 31. Since, as above stated, these pulses have afixed delay of 25 microseconds, the same saving can be effected by thearrangement of Fig. 6 as by the arrangement of Fig. 5. In Fig. 7 we haveagain indicated the exchange 12 and the lines 10, 11 of Fig. 1 leadingthereto. Three stations 32, 33 and 34 are shown looped from line 11 tothe doubled back end of conductor 10. Each loop is of a differentlength, the loop of station 32 being length dm, of station 33 being dp,and of station 34 being dt. Station 33 is the farthest removed from thecable and station 34 the nearest. The distance dp between station 33 andthe cable adds a delay of V being the speed of propagation of pulsesalong the loops. In order to avoid the necessity of changing the delaynetwork which is provided within a station and is characteristic of itssequential position, a loop may itself be provided with a delay networksuch as 35, 36 to balance the difference between dp and dm, or dp anddt, and thus re-establish the same electrical distance between eachstation and the cable.

We claim:

l. An intercommunication system of the kind described comprising anexchange network, a pulse transmitting line and a pulse receiving lineextending from said exchange, vand a plurality of substation setsconnected in parallel across said lines, each of said substation setsbeing arranged to receive a reference pulse and to receive a signalpulse at a predetermined time after said reference pulse, which time isdifferent from the corresponding time of any other substation, the sumof the length of the transmitting line between the exchange network andthe point of connection of a substation set to said transmitting lineand the length of the receiving line between the exchange network andthe point of connection of the substation set to said receiving linebeing the same for all substation sets.

2. An intercommunication system, according to claim 1, in which thesubstation sets are connected to the trans- 6 mitting line in apredetermined sequential arrangement and to the receiving line in areverse sequential arrangement.

3. An intercommunication system according to claim 1, in which the saidlines diverge from said exchange network aud have overlapping portionsat their extremities forming a return loop, and in which the substationsets are connected across said overlapping portions.

4. In an intercommunication system of the kind described, an exchangenetwork, a pulse receiving line and first and second pulse transmittinglines extending therefrom and forming two return loops, the pulsereceiving line being common to said loops, said pulse transmitting linesbeing of different lengths with said second line longer than said firstline, two subgroups of substation sets connected in parallel across saidreceiving line and said respective first and second transmitting lines,each group of substation sets being connected to said receiving line ina predetermined sequential arrangement and to a respective one of saidtransmitting lines in a reverse sequential arrangement, means fortransmitting reference pulses from said exchange over said firsttransmitting line and means for transmitting auxiliary reference pulsesover said second transmitting line with a delay shortened by theadditional time required for a pulse to traverse the second line ascompared to the first line, each of said substation sets being arrangedto receive a reference pulse and to receive a signal pulse at apredetermined time after said reference pulse, which time is differentfrom the corresponding time of any other substation.

5. In an intercommunication system of the kind described, an exchangenetwork, a pulse receiving line and a pulse transmitting line extendingtherefrom and forming together a return loop, two sub-groups ofsubstation sets connected in parallel across said receiving andtransmitting lines, said substation sets being connected to saidreceiving line in a predetermined sequential arrangement and to thetransmitting line in a reverse sequential arrangement, each of saidsubstations in a group having means for delaying a pulse passingtherethrough a predetermined time which is different from the delaysproduced by the other substations of the group, oppositely poledrectifiers inserted respectively in the parallel connections from thetwo subgroups of substation sets to said transmitting line, and meansfor transmitting alternate positive and negative reference pulses fromsaid exchange network over said transmitting line, said positive andnegative pulses having a time displacement equal to half the timesequence occupied by both subgroups of substation sets, each of saidsubstation sets being arranged to receive a reference pulse and toreceive a signal pulse at a predetermined time after said referencepulse, which time is different from the corresponding time of any othersubstation.

6. In an intercommunication system of the kind described, an exchangenetwork, a pulse receiving line and first and second pulse transmittinglines extending therefrom and forming a single return loop, said pulsetransmitting lines being of different lengths with said second linelonger than said rst line, a rst subgroup of substation sets connectedin parallel across said receiving line and said first transmitting line,a second subgroup of substation sets connected in parallel across saidreceiving line and said second transmitting line, said groups ofsubstation sets being connected to said receiving line in predeterminedsequential arrangements and to the respective transmitting lines inreverse sequential arrangements, each of said substations in the grouphaving means for delaying a pulse passing therethrough a predeterminedtime which is different from the delays produced by the substations ofthe group, rectifiers poled in one direction inserted in the parallelconnections of one half of the substation sets of both subgroups,rectifiers poled in the opposite direction inserted in the parallelconnections of the other half of the substation sets of both subgroups,and means for transmitting positive and negative reference pulses oversaid first and second transmitting lines having. a time displacementequal to one quarter of lthe time sequence occupied by both subgroups ofsubstation sets, each.. of said substation. sets being arranged toreceive a reference pulse and to receive a signal pulse at aVpredetermined time after said reference pulse,V which time is d'iterentfrom the corresponding` time of any other substation..

7. In an intercommunication system of the kindY described, an exchangenetwork, a pulse receiving line and a. pulse transmitting line extendingtherefrom and forming a single return loop, a plurality of sub-groups ofsubstation sets connected in parallel across said receiving line andsaid transmitting line, said substation sets being connected to saidreceiving line in a predetermined sequential ar,- rangement and to saidtransmitting*- line in. a reverse sequential arrangement, each of saidsubstations. in, a group having means for delaying a pulse passingtherethrough a predetermined time which is diferent from the delaysproduced by the other substations of the group, a filter tuned to acharacteristic carrier frequency connected in e the common parallelconnection for each subfgroup of substation sets, and means forcylically transmitting from said exchange network reference pulsessequentially modu lated at different carrier frequencies correspondingto the pass frequencies of. said lters. and having a time displacement.equal to the time lsequence occupied by all the sub-groups of substationsets divided by the number of sub-groups, each of. said. substation setsbeing arranged to receive a reference pulse and' to receive a signalpulse at a predetermined time after said' reference pulse, which timeisI different from tbecorresponding time of any other substation.

8. An intereommunication system according to claim 7 in which thetransmitting and receiving lines form a single return loop and saidsubstation sets are connected in loops connectedinparallelbetweensaidreceiving line and saidtransmitting line, adjustable, delay lines beinginserted in some of said loops to compensate for the differences in thelengths of the respective loops.

References Cited in the le of this patent Standard Handbook forElectrical Engineers, section 14, paragraph 2l-Knowltorr-7thf edition.

